The structure of the retina is critical to an animal ’ s ability to see in the dark . Retinas of vertebrate animals , including humans , have two different types of cells that are sensitive to light . Rods soak up the light while cones allow for color differentiation . The animals with the best night vision have an abundance of rods . Raccoons have an abundance of this trait . Their rods are very dense and tightly grouped , giving them superior vision in the dark .
A number of different birds see well at night , others not so much . Great blue herons , equipped with about five times the number of rods as a human has , have excellent night vision . Whippoorwills , goatsuckers , and night herons , in addition to the aforementioned owl , all welcome the nighttime .
Most animals who thrive at night , including deer , raccoons , coyotes , alligators , rodents , and foxes , possess a unique membrane on their eyes , the tapetum lucidum . Humans do not have this membrane . This layer of cells is located just behind the retina and acts as a mirror permitting more light into the eye . It is this membrane that makes their eyes appear as a bright yellowish-green glow when a direct light hits their eyes in the dark .
It is not just nocturnal wildlife that has this membrane . Dogs and cats possess the tapetum lucidum and see much better than we do when the sun goes down . Of course , in most cases , the dog ’ s greatest wish at night is to sleep , not hunt . Many night dwellers , including some with the allimportant tapetum lucidum membrane , must still rely on other senses to thrive . A mink is predominately nocturnal but has only fair nighttime vision . They must also employ their sense of smell to locate prey . Opossums hunt at night , but they rely as much on their noses as an addition to good eyesight to locate food . Too bad their sniffer doesn ’ t help them sense oncoming cars .
Animals without these features , the beady-eyed , the rodchallenged , or the tapetum lucidum-deprived , do not like to venture out at night as much . They are the Mr . Magoos of nighttime vision and prefer to stay at home when the sun disappears .
The ubiquitous gray squirrel doesn ’ t possess a tapetum lucidum and struggles to see at night much like humans do . They tend to venture out only when there is either man-made light present or under a lighter than normal sky from a particularly bright moon . Ironically , their cousin , the southern flying squirrel , is equipped with the tapetum lucidum membrane and is nocturnal , blessed with excellent nighttime vision .
The attributes that make many birds of prey successful hunters during the day , namely very dense cone structures within the eye , make for poor night time vision . Bald eagles and hawks stay close to home during the night , although they have been known to fly past dusk , employing their internal senses in addition to their eyesight to help guide them through the darkened sky .
As for the most beloved creature on Kiawah , the newly hatched loggerhead turtles ? They emerge from their eggs with blurry vision and instinctually use the moonlight to find the ocean . They have neither large eyes nor a tapetum lucidum . Their world exists off our shore , and their eyesight is designed very differently .
And what about that wolf that Little Red Riding Hood encountered ? He thrives at night , blessed with large eyes , an abundance of rods , and a tapetum lucidum . He is a master of nighttime vision . ( See accompanying sidebar for other night vision superstars .) That little girl should get back to the safety of her own home , preferably while the sun remains high in the sky overhead . NK
THE
SUPERSTARS OF NIGHT VISION
These animals possess some of the keenest nighttime vision in the entire animal kingdom :
Best night vision in each category :
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Birds : Owl . They can see up to 100 times better than a human in the dark .
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Domesticated animals : Cat . These animals have better night vision than dogs and need only about one-sixth as much light as humans do to see in the dark .
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Arachnids : Ogre-Faced Spider . They have six eyes and see better than an owl at night .
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Fish : Spookfish . They live at depths of . 6 to 1.2 miles beneath the surface of the water .
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Lizards : Leaf Tailed Geckos . They can see up to 350 times better than a human in the dark .
Photo by Larry Corio
WINTER / SPRING 2017 • VOLUME 37
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